1. Field of the Invention
The present invention relates to a method of configuring a packet-switched wireless access network for simultaneous use of a micro-mobility tunnelling-type protocol and a Quality of Service (QoS) routing protocol, to a packet-switched wireless access network for performing the method, to a router for use in the method, to an access router for use in the method, to a mobile node for use in the method, and to a method of manufacturing such a mobile node
2. Description of the Related Art
Many different requirements are expected of the network layer in all-IP access networks (e.g. 4G cellular networks). Two in particular are mobility and QoS. The former enables users to communicate seamlessly with remote network nodes via the Internet wherever they are, whereas the latter enables users to receive different levels of service for certain types of traffic. However, research has shown that problems may arise when attempting to configure an access network to operate a mobility protocol at the same time as a QoS routing protocol.
Best effort routing protocols such as Open Shortest Path First (OSPF) have been extended with QoS functionality. For example QoS Extensions to OSPF (QoSPF) (see RFC 2676) have been proposed in which the routing architecture of OSPF is augmented to include QoS-related link metrics e.g. the amount of bandwidth available at each link. Since OSPF (and therefore QoSPF) is an intra-domain link state routing algorithm, each router in the access network stores a database of the entire topology of the domain. Each router discovers its neighbouring routers and sub-networks, and advertises its local environment to other routers in the administrative scope of the network using a reliable flooding mechanism. These advertisements are stored and updated to synchronise routing knowledge in the network. The routers in the network may operate on an explicit route basis or on a hop-by-hop basis.
When operating a QoS routing algorithm it is prudent to operate some resource reservation system. For example a Bandwidth Broker may be used to admit a Reservation Request for a packet flow to travel a certain path across the access network. The Bandwidth Broker stores a database of the network topology and link state (based on the router advertisements for example). Using the database the Bandwidth Broker can decide whether or not to accept the Reservation Request. Therefore for hop-by-hop routing, although in principle the QoS route might be changed by routers on the path as new link state information is gained, this is not practical since a new Reservation Request would need to be made to the Bandwidth Broker. Accordingly, once the route is chosen for the session the hop-by-hop route does not change until a handover is performed.
Mobility at the network layer is concerned with maintaining the routability of packet data to and from a mobile node when that mobile node moves away from its home access network The main candidate for provision of this functionality is Mobile IP (MIP), Very briefly MIP relies on a Home Agent in the home access network to tunnel IP packets to the domain where the mobile node is attached. The mobile node forms a Care-of Address (CoA) that is globally topologically correct in the network to which it is attached. The Home Agent encapsulates packets that it receives addressed to the mobile node's home address in another IP packet addressed to the CoA. In this way packet data may still reach the mobile node even when it is away from the home network. Further details of Mobile IP can be found in RFC 3344, 3775 and 3776 to which reference is specifically made.
However, when a mobile node hands over to a new access router, binding updates are triggered to the Home Agent, etc. These binding updates can introduce unwanted delays and loss of packets, and thereby degradation in performance from the user's perspective. When attached to a particular wireless access network (such as a cellular network), a mobile node may change its point of attachment (i.e. access router) quite frequently (e.g. every few minutes or more often, particularly if on the move). Each change triggers configuration of a new CoA, followed by the necessary binding updates. Doing this frequently (e.g. every few minutes) is not practical
Hierarchical Mobile IPv6 (HMIPv6) has been proposed (see RFC 4140) to address this problem. HMIPv6 provides a mobility agent known as a Mobility Anchor Point (MAP) in the access network. A MAP is a logical entity that handles micro-mobility for the mobile node. Micro-mobility is a change in point of attachment of the mobile node from one access router to another, both of which are within the same domain of the access network. Whenever this happens, the mobile node sends a binding update to the MAP (comprising a new Link local CoA or LCoA), but the mobile node's primary CoA (or Regional CoA or RCoA) remains unchanged In this way the mobile node can move between access routers in the same administrative domain without having to send a binding update to the Home Agent. In contrast when the mobile node changes point of attachment to an access router in a different access network, this is a macro-mobility event i.e. requiring a binding update to be sent to the Home Agent of the mobile node
When an access network operates both a mobility protocol (such as HMIPv6) and a QoS routing protocol, the requirement for all packets to pass through a particular MAP in the domain breaks one QoS route (gateway to access router and vice versa) into two. In particular, due to the high volume of traffic that it handles, it is almost certain that the MAP does not lie on the best QoS route from the gateway to the access router. Even though two QoS routes are then calculated (gateway to MAP, MAP to access router), their combination is by definition not the best QoS route if the MAP does not lie on the route that would be computed between the gateway and the access router. This causes a routing conflict between mobility on the one hand and QoS routing on the other. Thus attempts to operate both tunnelling-type mobility protocols and QoS routing protocols at the same time have not produced the performance gains that might be expected.
We have realised that this places a constraint on the scalability of the architecture In particular, as more and more mobile nodes bind to a particular MAP (e.g. if more access routers are added to the MAP's domain), it will have to handle not only the micro-mobility binding updates for the mobile nodes, but also the new QoS route computation and Reservation Requests as each mobile node moves between access routers It is believed that this network architecture is not scalable to handle both mobility and QoS for the numbers of mobile nodes present in today's cellular networks for example, nor those expected in future access networks,.
“Analysis of cross issues between QoS routing and i-mobility protocols”, Friderikos, V. et al., IEE Proc.-Commun., Vol. 151, No. 3, June 2004, discusses some of the issues raised above. This document suggests that to address the conflict between tunnel-based micro-mobility protocols (such as HMIPv6) and QoS routing protocols, the path between the MAP and the AR could be lengthened by placing the mobility agent closer to the network edge (e.g. gateway). In this way it is suggested that problems associated with the two QoS tunnels mentioned above can be reduced. However, the scalability problem is not mentioned.